Idea 1) take gift bags that are first communion themed. Add tissue, place something heavy inside to make it stand up. You can even use candy. Tie balloons onto handle.

Idea 2) Take basket, pail anything that matches your theme, glue down foam inside and get personalized candy bars and picks to place in each. Add flowers or tissue to fill in gaps. (I do candy wrappers)

Idea 3) Make popcorn cake (recipes online). Take straws and poke in center and add air filled balloons to straws.

You can find a lot of great items that, with a little creativity and ingenuity will make great decorations for a first communion. First, look in the area where they have wedding decorations and favors -- especially white candles and candle holders. Also, bud vases and artifical flowers work well. Also, often you can find some really lovely Christian themed items -- I have found some really beautiful crystal crosses that would be great in a centerpiece. You may get lucky and even find something that is specifically themed for First Communion; part of the fun of the dollar store is that you never know what you'll find! Good luck, and congratulations on your little one's first communion, it is a wonderful reason to celebrate!